Flushing tanks on 382RK (2025)

[crwj40]

Hello Ally Family,
I am concerned with the way my two black water tanks empty. The Galley gray tank flushes great, but the two black tanks and the master bath gray tank are the problem. I have always flushed my black tanks first in every fifth wheel have owned, then the gray tank.
When I opened the master bath black tank, it starts off great but after about 30 seconds to a minute it is like there is a vacuum lock. After 20 mins of the black water flowing very slow, I noticed through the clear section at my discharge point, that the drain line is only halfway with water and flowing very slow. That has me thinking that it is not a venting issue. Solids are barely moving in the hose. It’s almost like there is not enough fall in the drain line to let it gravity flow properly.
I checked my auto level and also used a 4 foot level to check the rig. (It was perfect) I am concerned that it is not possible to get a good flush of my tanks.
I am not happy with the plumbing setup at all. The two black tanks cannot be filled separately, because of a “T” in the flush spray supply line. (Bad Design) The tanks should be capable of being cleaned out separately.
Has any one else had this issue or similar problems?
Please let me know your thoughts.
I do live in my rig full time.
Thanks
Chuck

 

[Oregon_Camper]

Have you gone up to the roof to see if the vent has a blockage?

Can someone open the toilet while you're outside looking, to see if that breaks the possible vacuum?

 

[BryanValRox]

Hello Ally Family,
I am concerned with the way my two black water tanks empty. The Galley gray tank flushes great, but the two black tanks and the master bath gray tank are the problem. I have always flushed my black tanks first in every fifth wheel have owned, then the gray tank.
When I opened the master bath black tank, it starts off great but after about 30 seconds to a minute it is like there is a vacuum lock. After 20 mins of the black water flowing very slow, I noticed through the clear section at my discharge point, that the drain line is only halfway with water and flowing very slow. That has me thinking that it is not a venting issue. Solids are barely moving in the hose. It’s almost like there is not enough fall in the drain line to let it gravity flow properly.
I checked my auto level and also used a 4 foot level to check the rig. (It was perfect) I am concerned that it is not possible to get a good flush of my tanks.
I am not happy with the plumbing setup at all. The two black tanks cannot be filled separately, because of a “T” in the flush spray supply line. (Bad Design) The tanks should be capable of being cleaned out separately.
Has any one else had this issue or similar problems?
Please let me know your thoughts.
I do live in my rig full time.
Thanks
Chuck

So, I will offer my option and a quick test for you to perform. Your description would certainly support that you have a venting problem BUT it could be a restriction problem as well.
Try this, when you get to the low flow condition have someone hold the toilet flush valve open so that air can enter the black tank via the toilet. If the flow corrects itself, you have a venting issue. If it doesn’t something is restricting your flow. Perhaps a drain valve that isn’t open or not staying open, or perhaps something floating in the plumbing that is restricting the flow.
We were testing our tanks and valves in the driveway prior to any use and flushed a tank plumbing cut out blank out of one of the tanks. I doubt “Fall” has anything to do with your issue. Your tanks are inside the the frame rails and your discharge outlet is lower, so gravity will always work for you.

 

[crwj40]

Have you gone up to the roof to see if the vent has a blockage?

Can someone open the toilet while you're outside looking, to see if that breaks the possible vacuum?

Have you gone up to the roof to see if the vent has a blockage?

Can someone open the toilet while you're outside looking, to see if that breaks the possible vacuum?

Thanks,
kinda on my own. but great idea, I’ll see if I can get neighbor to help with that.

 

[crwj40]

So, I will offer my option and a quick test for you to perform. Your description would certainly support that you have a venting problem BUT it could be a restriction problem as well.
Try this, when you get to the low flow condition have someone hold the toilet flush valve open so that air can enter the black tank via the toilet. If the flow corrects itself, you have a venting issue. If it doesn’t something is restricting your flow. Perhaps a drain valve that isn’t open or not staying open, or perhaps something floating in the plumbing that is restricting the flow.
We were testing our tanks and valves in the driveway prior to any use and flushed a tank plumbing cut out blank out of one of the tanks. I doubt “Fall” has anything to do with your issue. Your tanks are inside the the frame rails and your discharge outlet is lower, so gravity will always work for you.

Bryan, thank you sir.
Think I’m gonna go get a camera scope to look at the possible restricted flow. I have the electric gate valves and that is all new to me. I’m an old school kinda guy and takes me some time to trust new technology. LOL
Thanks again
Chuck